In recent years, fuel cells have been focused upon as energy sources for addressing global environmental problems and energy problems. In particular, since solid polymer electrolyte fuel cells can operate at low temperatures and can be reduced in size and weight, applications thereof to residential fuel cell and fuel cell for vehicles have been studied.
A separator is one of important components of a general solid polymer fuel cell. Characteristics required for the separator include excellent corrosion resistance in an acidic solution, high mechanical strength with respect to vibration and the like, low contact resistance between the separator and carbon paper for anode and cathode electrodes, easily in groove processing and the like, being lightweight, and low costs.
Recently, metal plates such as a stainless steel plate have been mainly studied as a substrate of a separator that has the above characteristics. In a separator using a metal such as stainless steel, titanium, or an alloy thereof, when an anti corrosion film is formed on a surface, corrosion resistance is obtained, but it is not necessarily sufficient. In addition, it is known that, since an anti corrosion film increases contact resistance between the separator and anode electrode and between the separator and cathode electrode, conductivity deteriorates and power generation efficiency of a fuel cell decreases. In addition, since materials such as stainless steel, titanium, or an alloy thereof are expensive, there are serious problems in practicality for, for example, a vehicle fuel cell.
Meanwhile, while the metals aluminum and magnesium have been studied as a lightweight and inexpensive separator substrate, it is known that, since an insulating oxide film is likely to be formed on a surface of a substrate, corrosion resistance is not likely to be sufficient, eluted ions are likely to deteriorate catalyst characteristics, and the ion conductivity of a solid polymer film is likely to be reduced, and as a result, power generation characteristics deteriorate.
In addition, the above-described problems may also occur similarly in a current collecting member for a fuel cell.
Patent Literature 1 discloses a technology for a separator for a fuel cell including a coating layer having an amorphous carbon layer and a conductive portion on a metal substrate. The separator includes an insulating amorphous carbon layer and a coating layer that includes an amorphous carbon layer and a conductive portion formed of graphite fine particles.
In order to improve corrosion resistance of an aluminum material, Patent Literature 2 discloses a technology for a separator for a fuel cell in which a copper layer is formed on a surface of a substrate made of pure aluminum or an aluminum alloy using a wet plating method, a tin layer is laminated on the surface using a wet plating method, and a metal layer made of one or more metals selected from the group consisting of titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten or an alloy based on these metals is further incorporated using a dry deposition method such as vacuum deposition.
In addition, Patent Literature 3 discloses a technology for a separator for a fuel cell in which an aluminum substrate, a zinc layer that is directly formed on the substrate and contains zinc particles having a particle size of less than 0.1 μm, a nickel plating layer that is directly formed on the zinc layer, and a conductive resin layer that is directly formed on the nickel plating layer and contains scaly or needle-like graphite particles having a long diameter of 1 μm to 100 μm are laminated with thicknesses of 5 μm to 30 μm.